1. Field of the Invention PA1 an applicator for direct application of a liquid or pasty medium on one side of the traveling material web, PA1 a rotating mating surface carrying the traveling material web along a contact section, and PA1 a press roll rotating relative to the mating surface in opposite direction and serving to press liquid or pasty medium applied on one side of the material web into the traveling material web. PA1 a second mating face rotating in a direction opposite to that of the first mating face and, based on the pass-through direction of the material web, following said mating face at a distance, with the traveling material web being carried on the surface of the second mating face along a contact section in a manner such that the material web side provided already with the medium bears on the surface, PA1 a second applicator for direct application of a liquid or pasty medium on one side of a traveling material web, and PA1 a second press roll rotating in a direction opposite to that of the second mating face and serving to press liquid or pasty medium applied on one side of the traveling material web into the traveling material web. PA1 an applicator for direct application of a liquid or pasty medium on one side of the traveling material web, PA1 a rotating mating face on the surface of which the traveling material web is carried along a contact section, PA1 a press roll rotating in a direction opposite to that of the mating face and serving to press liquid or pasty medium applied on one side of the material web into the traveling web, and PA1 a press roll mating roll rotating in a direction opposite to that of the press roll. PA1 a second mating face rotating relative to the first press roll in the same direction and following said mating face at a distance, based on the pass-through direction of the material web, with the traveling material web being carried on the surface of the second mating face along a contact section in a manner such that the side of the material web provided already with the medium bears on the roll surface, PA1 a second applicator for direct application of a liquid or pasty medium on one side of a traveling material web, PA1 a second press roll rotating relative to the second mating face in opposite direction and serving to press liquid or pasty medium applied on one side of the material web in the traveling material web, and PA1 a second press roll mating roll rotating in a direction opposite to that of the second press roll. PA1 two applicators (which may be of the same type) each of which applies a liquid or pasty medium directly on one of the two sides of the traveling material web, and PA1 two press rolls of same type that rotate in opposite directions and each of which presses the liquid or pasty medium applied on the relevant one of the two sides of the material web into the traveling material web. PA1 an open-jet nozzle applicator for direct application of a liquid or pasty medium on one side of a traveling material web, PA1 a rotating press roll for pressing liquid or pasty medium applied on one side of the material web into the traveling material web, and PA1 a press roll mating roll that rotates in a direction opposite to that of the press roll.
The present invention relates to a method and apparatus for application of a liquid or pasty medium on a traveling material web, notably of paper or cardboard.
2. Description of the Related Art
An apparatus for application of a liquid or pasty medium on a traveling material web working in compliance with a conventional method is known, e.g., from U.S. Pat. No. 4,848,268. In this apparatus, two applicator rolls rotating in opposite directions form between themselves a press nip through which the traveling material web passes. Assigned to each applicator roll is an applicator mechanism which applies the liquid or pasty medium via an applicator pressure chamber and a doctor on the surface of the applicator roll. The medium applied on the applicator roll surface is then carried, due to the rotation of the applicator roll, in the press nip between the two applicator rolls. There, the medium is transferred from the roll surface to the relevant side of the material web and pressed at the same time into the material web. This method of application is called indirect application. With both applicator mechanisms in operation, the traveling material web is in this way coated on both sides with the liquid or pasty medium. In another embodiment of the this prior apparatus, also described in U.S. Pat. No. 4,848,268, the pressure chamber applicators are replaced by such forming a sump with an exposed liquid surface and applying the medium from the sump via a doctor on the surface of the applicator roll.
While good results as such are achieved with this indirect application method and pertaining applicators, contaminations are able to separate out of the paper or cardboard of the material web as the medium is pressed in the material web in the press nip, however, and accumulate on the surface of the applicator rolls. This can happen especially with material webs consisting predominantly of recycled paper. Such contaminations accumulated on the roll surface then soil the applicators and can ultimately striate the application film on the applicator roll surface, which striae will then be visible also on the product, i.e., on the coated material web.
What is needed in the art is a method and apparatus enabling the high-quality application of a liquid or pasty medium on a traveling material web, without contaminations contained in or on the material web being able to degrade the quality of application.